Rotating element sheet material has been disclosed in U.S. Pat. Nos. 4,126,854 and 4,143,103, both hereinabove incorporated by reference, and generally comprises a substrate, an enabling fluid, and a class of rotatable elements. As discussed more below, rotating element sheet material has found a use as “reusable electric paper.” FIG. 1 depicts an enlarged section of rotating element sheet material 50, including rotatable element 10, enabling fluid 20, cavity 30, and substrate 40. Observer 60 is also shown. Although FIG. 1 depicts a spherically shaped rotatable element and cavity, many other shapes will work and are consistent with the present invention. As disclosed in U.S. Pat. No. 5,389,945, herein incorporated by reference, the thickness of substrate 40 may be of the order of hundreds of microns, and the dimensions of rotatable element 10 and cavity 30 may be of the order of 10 to 100 microns.
In FIG. 1, substrate 40 is an elastomer material, such as silicone rubber, that accommodates both enabling fluid 20 and the class of rotatable elements within a cavity or cavities disposed throughout substrate 40. The cavity or cavities contain both enabling fluid 20 and the class of rotatable elements such that rotatable element 10 is in contact with enabling fluid 20 and at least one translational degree of freedom of rotatable element 10 is restricted. The contact between enabling fluid 20 and rotatable element 10 breaks a symmetry of rotatable element 10 and allows rotatable element 10 to be addressed. The state of broken symmetry of rotatable element 10, or addressing polarity, can be the establishment of an electric dipole about an axis of rotation. For example, it is well known that small particles in a dielectric liquid acquire an electrical charge that is related to the Zeta potential of the surface coating. Thus, an electric dipole can be established on a rotatable element in a dielectric liquid by the suitable choice of coatings applied to opposing surfaces of the rotatable element about an axis of rotation.
The use of rotating element sheet material as “reusable electric paper” is due to that fact that the rotatable elements are typically given a second broken symmetry, a multivalued aspect, correlated with the addressing polarity discussed above. That is, the above-mentioned coatings may be chosen so as to respond to incident electromagnetic energy in distinguishable ways, as indicated in FIG. 2, for example. Thus, an applied vector field can control the aspect of rotatable element 10 to favorably situated observer 60.
For example, as disclosed in U.S. Pat. No. 4,126,854, hereinabove incorporated by reference, rotatable element 10 may comprise a black polyethylene generally spherical body with titanium oxide sputtered on one hemisphere, where the titanium oxide provides a light-colored aspect in one orientation. Such a rotatable element in a transparent dielectric liquid will exhibit the desired addressing polarity as well as the desired aspect.